Offset printing presses are well known in the art. Typically, water and ink are supplied to a printing plate cylinder, and are then transferred to a blanket cylinder for printing onto sheets or web, fed between the blanket cylinder and an impression cylinder. The water supply to the plate cylinder usually comprises a dampening unit having a dampening form roller which contacts the plate cylinder and is fed water from a water pan through intermediate water transferring rollers. Similarly, an inking unit transfers ink through one or more ink form rollers contacting the plate cylinder, the ink form rollers receiving ink from an ink supply through a series of ink transfer rollers.
While such presses have fixed lateral dimensions, and as such printed products wider than the length of the cylinders cannot be produced, the circumference of the rotating cylinders determines the length of each repeated pattern being printed onto the web or sheets passing therethrough. Accordingly, the larger the circumference of the plate and blanket cylinders being used, the longer the printed pattern that can be produced. Therefore, in order to permit a press to be modified to permit printing of different lengths of printed patterns, standard variable size presses provide a changeable insert comprising plate, blanket and impression cylinders. Replacement inserts comprising cylinders of different diameters can therefore be used with the same press.
An important parameter determining printing quality is the line of contact between two cylindrical rollers in contacting engagement, otherwise known as the contact stripe. Standard adjustment mechanisms between rollers and cylinders include mechanical means such as bolts or screws and single pneumatic actuators, to allow fine tuning of the contact stripe between, for example, the inking or dampening form roller and the plate cylinder. However, conventional adjustment mechanisms are usually adapted to be used with plate and blanket cylinders of fixed diameter.
On standard variable size presses, mechanical stoppers are usually included in the insert in order to adapt the adjustment mechanisms of the form rollers and cylinders to the plate and blanket cylinder diameter. Such stoppers offer only an adjustment having a limited precision.
Sleeve offset presses, such as the one disclosed in U.S. Application No. 60/457,295 by the applicant and incorporated herein by reference, provide for replacing only the plate and blanket cylinders, thereby eliminating the need for the various inserts. While the elimination of the inserts minimizes the complexity of changing cylinder sizes and reduces the storage space previously required for replacement inserts, it also eliminates the support for the prior mechanical stoppers. Integrating the stoppers directly on the cylinder bodies greatly increases their weight and cost. Alternatively, providing a different adjustment mechanism for each cylinder size can be very costly as well as increase the storage space necessary for spare parts and the down time when the cylinders are changed.
Accordingly, there is a need for a unique adjustment mechanism providing an adequate contact stripe adjustment between rolling elements in a printing press and being able to accommodate various dimensions of plate and blanket cylinders.